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* The  Comparative  Morphology  ol  the 

I': 

Genitalia  of  Insects 

by 


ANNA  GRACE  NEWELL 

B.  A.  Smith  College,  1900 
M.  A.  Smith  College,  1908 


THESIS 


Submitted  in  Partial  Fulfillment  of  the  Requirements  for  the  Degree  of 
DOCTOR  OF  PHILOSOPHY 

In  Entomology 


in  the  Graduate  School  of  the  University  of  Illinois 

1916 


Reprinted  from  the  Annali  of  the  Entomological  Society  of  America 
Vol.  XI,  No.  2,  June,  1918 


5 DlRtCf 


BIOGRAPHY 


S O 1 1 L - 
|v/4^,c- 


The  candidate  was  born  December  23,  1876,  in  Flint, 
Michigan,  and  most  of  the  work  covered  in  the  grammar  grades 
was  done  in  that  city.  Preparation  for  college  was  received  in 
4,  the  High  School  at  Batavia,  New  York,  and  the  following  four 
^ years  were  spent  at  Smith  College,  from  which  the  degree  of 
g B.  A.  was  received  in  June,  1900. 

In  1907  the  candidate  was  appointed  instructor  in  Zoology 
at  Smith  College  and  in  1916  was  made  Assistant  Professor  in 
the  same  subject.  The  intervening  years  between  1900  and 
^ 1907  were  spent  partly  as  a substitute  at  Smith  College  in  the 

yy  Zoology  Department,  partly  at  home,  and  in  Europe  for  the 

fs'  year  1906-07,  during  which  one  semester  was  spent  in  the  study 
of  Zoology,  at  the  University  of  Leipzig. 

Work  in  Entomology  was  done  at  Cornell  University,  under 
Professor  A.  D.  McGillivray,  during  the  summer  sessions  of 
1908  and  1909,  as  well  as  for  the  year  1914-15  at  the  University 
of  Illinois.  The  second  minor  subject.  Ecology,  was  studied  at 
the  summer  laboratory  of  the  University  of  Montana  in  1913, 
under  Dr.  C.  C.  Adams  and  under  Professor  V.  E.  Shelford,  at 
the  University  of  Chicago,  in  the  summer  quarter,  1914. 


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in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


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THE  COMPARATIVE  MORPHOLOGY  OF  THE 
GENITALIA  OF  INSECTS.* 

Anna  Grace  Newell,  Ph.  D. 


I,  Introduction. 

1.  Somites. 

2.  Theories  and  Investigators. 

3.  Posterior  Somites. 


II.  Investigation. 

1.  General  Principles. 

2.  Method  of  Preparation. 

3.  Discussion  and  Tables: 

a.  Thysanura. 

b.  Orthoptera. 

c.  Hemiptera. 

d.  Neuroptera. 

e.  Mecoptera. 


III.  Summary. 

1.  Somite  Eight. 

2.  Somite  Nine. 

3.  Somite  Ten. 

4.  Somite  Eleven, 


IV.  Bibliography. 


V.  Explanation  of  Plates. 


VI.  Plates. 


4.  Genitalia. 

5.  Cerci. 

6.  Acknowledgments. 


f.  Trichoptera. 

g.  Coleoptera. 

h.  Lepidoptera. 

i.  Diptera. 

j.  Hymenoptera. 

5.  General  Statement. 

6.  Appendage  I. 

7.  Appendages  II  and  III. 

8.  Appendage  IV. 


I.  INTRODUCTION. 

1.  Somites. — The  third  and  caudal  region  of  those  into 
which  an  insect  is  divided  is  called  the  abdomen.  Here,  for  the 
most  part,  the  segments  of  which  it  is  composed  show  a simple 
and  almost  primitive  structure.  In  the  adult  a typical  segment, 
more  properly  designated  a somite,  consists  of  a dorsal  chitinized 
portion  or  sclerite,  called  the  tergum,  and  a ventral  sclerite,  or 
sternum.  These  are  connected  laterally  by  arthrodial  mem- 
branes, conjunctiva  or  pleura,  in  each  one  of  which  is  a spiracle. 
There  are  exceptions  to  this  arrangement  at  both  cephalic  and 
caudal  ends,  with  the  greater  complexity  at  the  latter.  No 

* Contribution  from  the  Entomological  Laboratories  of  the  University  of 
Illinois,  No.  51. 


109 


no 


Annals  Entomological  Society  of  America  [Vol.  XI 


spiracles  are  ever  present  eaudad  of  the  eighth  somite,  and,  in 
most  cases,  where  the  somites  eaudad  of  the  seventh  are 
retracted,  spiraeles  are  laeking  in  the  eighth.  Therefore  it  is 
evident  that  the  adult  abdomen  always  presents,  to  the  eye  at 
least,  a far  more  simple  eomposition  than  do  the  head  and 
thorax.  In  reality,  in  many  larvae  an  abdominal  somite  is  an 
entire  ring  without  differentiation  into  tergite  or  sternite,  an 
arrangement  often  seen  in  the  lower  thoracic  somites,  and  a 
more  nearly  primitive  one  than  that  above  mentioned. 

• The  general  shape  of  the  abdomen,  taken  as  a whole,  also 
varies  considerably.  Aeeording  to  the  best  authorities,  one 
ought  to  reeognize  the  abdomen,  systematically,  from  the 
number  of  its  somites  and  from  its  appendages.  The  fact  sug- 
gested above,  that  the  eaudal  somites  may  be  more  or  less,  even 
entirely,  eoncealed  by  retraction,  is  responsible  for  the  number- 
ing of  abdominal  somites  which  is  based  only  upon  the  number 
of  visible  somites  and  has  no  justifieation  in  morphology.  Dis- 
agreement upon  this  point  is  found,  however,  not  only  among 
the  systematists,  who  formerly  limited  themselves  to  numbering 
the  abdominal  somites  whieh  were  undoubtedly  visible,  but  also 
among  the  morphologists.  The  latter  differ  in  their  results  for 
various  reasons,  as  follows:  (1)  Beeause  of  the  loss  of  certain 
sclerites.  (2)  Beeause  of  differences  in  the  point  of  view:  e.  g., 
some  investigators  begin  to  count  at  the  eephalie,  while  others 
begin  at  the  caudal  end  of  the  abdomen,  and  still  others  do  not 
correlate  closely  dorsal  and  ventral  selerites.  (3)  Beeause, 
undoubtedly,  of  failure  to  observe  the  selerites  present  in  the 
caudal  region,  due  in  many  eases  to  the  laek  of  potash  or  other 
suitable  reagents  and  methods  for  exposing  ehitinized  parts. 

2.  Theories  and  Investigators. — There  follows  at  this 
point  a list  of  prominent  investigators  together  with  the  number 
of  abdominal  somites  whieh  they  have  believed  were  present 
in  the  adults  of  certain  orders: 

Orthoptera. 


1872  Chadima 11  abdominal  somites 

1876  Brunner  von  Wattenwyl 9 abdominal  somites 

1882  Tarzioni-Tozzetti 11  abdominal  somites 

COLEOPTERA. 

1894  Peytoureau  (in  Hydrophilus) 8 abdominal  somites 

1894  Peytoureau  (in  Dytiscus) 9 abdominal  somites 

1893  Kolbe  (in  lamellicomia) 9 abdominal  somites 

1893  1894  1896  Verhoeff 10  abdominal  somites 

1903  Berlese  (in  Coleoptera  in  general) 11  abdominal  somites 


1918] 


Morphology  of  Genitalia  of  Insects 


111 


Hemiptera. 

1893  1894  1896  Verhoeff 11  abdominal  somites 

Lepidoptera. 

9 abdominal  somites 

9 abdominal  somites 

10  abdominal  somites 

At  least  10  abdominal  somites 


Trichoptera. 

1849-53  Lacaze-Duthiers,  typical  number  in  insects 11  abdominal  somites 

1886  1888  Grassi,  typical  number  in  insects 10  abdominal  somites 

1901  Zander 13  abdominal  somites 


From  investigations  on  Thysanura,  according  to  Grassi, 
there  are  10  abdominal  somites  besides  ‘‘ein  Afterstiick,  das 
allerdings  nicht  mehr  als  Segment  aufzufassen  ist;”  according 
to  C.  Brunner  von  Wattenwyl,  this  is  a terminal  segment, 
welches  aus  den  drei  Afterklappen  und  den  seitlich  inserirten 
“Anhangseln  (Cerci)  gebildet  wird.” 

Berlese  concludes  his  discussion  of  the  matter  by  saying 
that  the  entire  number  of  abdominal  somites  varies  from  nine 
to  eleven,  except  for  the  Collembola,  which  he  considered 
aberrant,  this  reduction  taking  place  from  the  lower  to  the 
higher  orders,  and  at  the  caudal  as  well  as  at  the  cephalic  end 
of  the  abdomen.  He  states  emphatically  that  eleven  is  not 
exceeded,  aside  from  the  telson  with  its  rudiments,  found  only 
in  certain  of  the  Thysanura  and  immature  Orthoptera,  and  he 
therefore  would  consider  eleven  as  the  typical  number. 

Certain  other  investigators,  represented  mainly  by  Hey- 
mons,  uphold  the  view  that  the  primitive  number  of  abdominal 
segments  is  twelve;  the  twelfth,  just  as  much  as  the  eleven 
cephalad  of  it,  containing  a caelomatic  cavity.  Heymons  calls 
this  twelfth  somite  the  telson,  and  his  evidence  for  it  is  found 
mainly  in  certain  Thysanura,  where  he  identifies  it  with  a small 
sclerite,  called  by  many  the  supra-anal  plate,  situated  between 
the  eleventh  ter  git  e and  the  anus.  He  also  describes  it  in 
immature  Acridid^,  Locustidae,  and  Gryllidae  as  a triangular 
plate  separated  from  the  eleventh  tergite,  to  which  it  forms  the 
apex,  by  a suture.  In  the  adults  of  some  Acrididse  this  plate 
becomes  totally  fused  with  the  eleventh  tergite.  In  this  case 
the  terminal  segment  is  commonly  called  the  eleventh  only, 
instead  of  the  eleventh  and  twelfth,  according  to  Heymons. 
Berlese  gives  another  example  of  the  twelfth  tergite  in  Acrida 
turrita  L.,  a form  not  studied  by  Heymons.  (Plate  VI,  Figs.  1, 
10,  13,  and  17  t 12.) 


1832  Burmeister. 

1893  Kolbe 

1894  Peytoureau 
1903  Berlese.  . . . 


112 


Annals  Entomological  Society  of  America  [Vol.  XI 


According  to  Haase,  the  eleventh  is  not  an  autonomous 
somite,  and  Verhoeff  agrees  with  him.  Dewitz  states  that  the 
eleventh  somite  is  formed  only  by  the  doubling  of  the  tenth, 
and  he  says  that  in  Decticus  this  only  occurs  after  hatching. 
Wheeler  shows  and  labels  eleven  segments  in  all  the  figures  in 
his  well  known  embryological  investigations. 

3.  Posterior  Somites. — The  first  traces  of  segmentation 
are  found  very  early  in  the  germ-band  of  the  insect,  which 
becomes  divided  by  transverse  grooves  into  somites.  This 
process,  Heider  maintains,  even  precedes  gastrulation  in 
Hydrophilus.  This  is  not  a primitive  condition  however.  In 
the  completely  segmented  germ-band,  Korschelt  and  Heider 
state,  there  are  ten  abdominal  somites  in  addition  to  the  telson, 
and  they  give  the  following  observations  on  the  germ-bands  of 
various  forms,  in  proof  of  this  statement : Heider,  on  the  germ- 
band  of  Hydrophilus;  Graber,  on  Lina,  Stenobothrus,  various 
Lepidoptera  and  Hylotoma;  Wheekr,  on  Doryphora  and 
Blatta;  Cholodkovsky,  on  Blatta;  and  Carriere  on  Chalicodoma. 

In  looking  over  the  plates  belonging  to  all  the  articles 
referred  to  by  Korschelt  and  Heider,  in  each  of  the  above  cases, 
one  sees  that  in  the  large  number  of  germ-bands  figured  the 
terminal  abdominal  somite  is  always  numbered  eleven,  and  that 
in  no  case  is  the  term  telson  used,  that  being  the  name  given  by 
Heymons  to  the  twelfth  abdominal  somite.  Of  course,  mor- 
phologically, what  these  somites  are  labeled  may  seem  imma- 
terial, and  fundamentally  it  is.  However,  there  is  no  doubt 
that  considerable  confusion  has  arisen  from  Korschelt  and 
Heider’s  statement  in  this  regard.  Many  invariably  take  it 
that,  according  to  these  authors,  the  insect  abdomen  is  typ- 
ically composed  of  ten  somites  and  no  more.  Others  may 
understand  that  the  telson  mentioned  is  formed  of  the  eleventh 
and  twelfth  somites  fused.  As  one  can  see  from  the  work  of  the 
investigators  themselves,  they  agree  in  giving  eleven  as  the 
typical  number  of  abdominal  somites  in  the  germ-bands  of  the 
insects  upon  which  they  worked. 

One  of  the  difficulties  in  arriving  at  any  conclusion  from  the 
foregoing  is  that  so  few  investigators  have  traced  structures 
from  embryonic  through  larval  to  adult  stages,  and  this  same 
difficulty  confronts  us  when  we  review  the  work  done  on  the 
genital  appendages. 


1918] 


Morphology  of  Genitalia  of  Insects 


113 


A marked  deviation  from  the  primitive  condition  is  found  in 
the  lack,  apparent,  at  least,  of  appendages  on  the  adult  abdom- 
inal somites.  If  one  looks  at  the  germ-band  of  an  insect,  how- 
ever, one  can  see,  soon  after  the  appearance  of  the  appendages 
of  the  head  and  thorax,  anlages  of  a pair  of  appendages  for  each 
somite  of  the  abdomen  also.  These  rudiments  are  lateral,  sac- 
like  swellings,  usually  pointing  backward,  and  generally  consid- 
ered as  serially  homologous  with  the  thoracic  legs,  as  also  with 
the  appendages  of  the  head. 

The  first  account  of  embryonic  limb  rudiments  on  the  first 
abdominal  somite  of  Gryllotalpa,  was  written  by  Rathke  in 
1844,  and,  later,  on  all  the  abdominal  somites,  by  many  others. 
As  we  mean  by  primitive,  in  insects,  that  which  shows  their 
close  relationship  to,  and  probable  descent  from,  a myriapod- 
like form  consisting  of  several,  successive,  similar  somites,  each 
having  a pair  of  appendages,  we  are  interested  to  look  in  the 
adult  for  traces  of  the  embryonic  condition  described  above. 

4.  Genitalia. — There  is,  at  the  caudal  end  of  the  abdomen 
of  every  insect,  a group  of  appendages  having  to  do,  more  or 
less  directly,  with  the  function  of  reproduction.  Three  pairs  of 
these  appendages  taken  together  are  called,  in  a general  way, 
by  German  authors,  “ Geschlechtsanhange  ” ; by  English  and 
American  ones,  ‘'genital  appendages,”  “genitalia,”  or  “gona- 
pophyses,”  the  latter,  a term  introduced  by  Huxley  in  connection 
with  the  Crustacea,  and  used  by  many  others  to  indicate  part 
or  all  of  these  structures,  in  one  or  both  sexes.  They  have  also 
been  given,  individually,  names  differing  from  one  another  in, 
and  characteristic  of,  each  order,  so  that  in  some  cases  only  a 
systematist  of  the  group  concerned  could  follow  a description 
using  them.  These  three  pairs  of  appendages  have  been  attrib- 
uted to  the  three  somites  cephalad  of  the  terminal  or  anal 
somite,  which,  as  explained  in  the  foregoing,  is  considered  the 
eleventh  by  some  and  the  tenth  by  others. 

It  would  seem  natural  to  homologize  these  appendages  with 
the  anlages  of  legs  found  respectively  on  the  same  somites  of 
the  embryonic  germ-band,  but  there  are  at  least  two  opposed 
views  on  this  question.  Lacaze-Duthiers,  who  published  papers 
on  the  subject  in  1849-52,  did  not  so  consider  them,  but  regarded 
them  as  modified  ventral  sclerites  of  their  respective  urites,  the 
latter  being  the  name  by  which  this  author,  followed  in  this 
respect  by  Berlese  and  others,  called  the  abdominal  somites. 


114 


Annals  Entomological  Society  of  America  [Vol.  XI, 


Haase,  much  later,  also  stated  that  the  gonapophyses  were  not 
true  appendages,  but,  to  translate,  ‘dntegumental  structures  of 
a somewhat  higher  order  than  styles,”  meaning  those  styles 
which  are  inserted  at  the  bases  of  the  legs,  in  the  coxae  of  some 
Myriapods  and  Thysanura.  Grassi  in  1889  held  a similar  view. 
According  to  Wheeler,  all  these  investigators  based  their  con- 
clusions solely  upon  comparative  anatomical  data.  The  fol- 
lowing investigators,  however,  have  regarded  these  appendages, 
genitalia  or  gonapophyses,  as  homologous  with  the  true,  so-called 
"'ambulatory,”  "segmental,”  or  "pedal”  extremities,  although 
they  have  differed  a good  deal  in  the  details  of  their  explana- 
tions: Weismann  in  1866;  Kraepelin  in  1872;  Kowalevsky  in 
1873;  Dewitz  in  1875 ; Huxley  in  1877 ; Cholodkovsky  in  1891; 
and  Wheeler  in  1893. 

Korschelt  and  Heider  state  their  point  of  view  as  follows: 
"We  are  here  led  to  ask  to  what  extent  the  external  genital 
appendages,  the  so-called  gonapophyses,  are  to  be  traced  back 
to  limb  rudiments.  The  researches  of  Kraepelin  and  Dewitz 
have  revealed  that  the  ovipositors  of  the  Hymenoptera  and  the 
Locustidae,  and  the  corresponding  genital  appendages  of  the 
male  in  these  forms,  are  derived  from  the  imaginal  discs  of  the 
eighth  and  ninth  abdominal  somites,  which,  when  they  first 
appear  in  the  larva,  closely  resemble  the  imaginal  discs  of  the 
larva  of  Corethra,  which  yield  the  thoracic  limbs.”  (p.  371.) 
Butschli  and  others  have  therefore  attempted  to  refer  the  gona- 
pophyses of  these  forms  to  true,  abdominal  limb-rudiments. 
"In  support  of  this  assumption,  we  might  point  out,”  continue 
Korschelt  and  Heider,  "that  these  imaginal  discs  develop  from 
the  abdominal  rudiments  present  in  the  embryo.”  "It  should, 
however,  be  mentioned,”  they  assert,  "that  Haase,  following 
Uljanin,  has  recently  opposed  this  view,  although,  as  it  appears 
to  us,  with  insufficient  reason,  maintaining  that  the  gona- 
pophyses should  be  regarded  merely  as  secondarily  acquired, 
external  appendages.” 

Heymons  is  one  of  the  strongest  opponents  of  a homology 
between  the  genital  appendages  and  the  anlages  of  the  seg- 
mental ambulatory  ones  of  the  embryo  and  the  appendages  of 
an  ancestral  form.  He  states  in  a resume  published  in  1899  that 
after  embryological  investigations  on  a great  number  of  species 
of  Locustid®,  Gryllid®,  and  Hemiptera,  he  has  come  to  the 
conclusion  that  it  is  a fundamental  principle,  in  the  study  of 


1918]  Morphology  of  Genitalia  of  Insects  115 

insect  embryology,  that  there  is  present  no  genetic  relationship 
between  the  embryonal  anlages  of  the  ambulatory  appendages 
and  the  gonapophyses. 

The  entirely  different  results  obtained  by  Wheeler,  from  his 
embryological  work  on  Xiphidium,  Heymons  attributes  to  the 
fact  of  an  unusually  early  origin  of  the  genitalia  in  Xiphidium 
and  other  Locustidae,  even  as  early  as  the  embryonal  period 
before  the  atrophy  of  the  anlages  of  the  segmental  appendages. 
Also,  in  addition  to  this  fact,  Heymons  lays  emphasis  upon  the 
very  small  size  of  the  sternites  in  Locustidae,  which  would  very 
easily  lead  one  to  confuse  the  embryonic  limb-rudiments  and 
the  developing  genitalia  or  gonapophyses ; while  in  other 
forms,  he  states,  the  sternites  are  much  larger.  In  fact,  Hey- 
mons asserts,  from  his  investigations  on  Lepisma  saccharina  and 
certain  Hemiptera,  that  the  sexual  appendages  do  not  originate 
even  in  the  same  parts  of  the  sternites  where  the  above-men- 
tioned anlages  of  segmental  appendages  are  found.  It  seems 
unbelievable  that  an  investigator  who  has  had  as  much  experi- 
ence as  Wheeler  in  the  examination  of  insect  embryos  should 
have  made  the  mistake  attributed  to  him  by  Heymons. 

The  anlages  of  segmental  appendages  on  the  middle  and 
cephalic,  as  well  as  on  the  caudal  somites,  degenerate  during 
the  embryonic  stages,  and  some  authors,  Goosens  and  Knatz, 
for  example,  have  thought  that,  for  this  reason,  the  prolegs  of 
caterpillars  first  develop  during  larval  life.  To  quote  again 
from  Korschelt  and  Heider:  '‘We  should  here  have  to  suppose, 
as  Graber  also  has  pointed  out,  an  embryonic  rudiment  remain- 
ing for  a considerable  time  in  a dormant  condition.  On  the 
whole,  the  embryonal  data  seem  to  support  the  view  of  Balfour 
which  Cholodkovsky  adopted,  and  to  which  Graber  was 
inclined,  that  the  abdominal  appendages  of  the  Lepidoptera  and 
Hymenoptera  are  to  be  regarded  as  true  limbs.  We  have  already 
had  several  examples,  in  the  Crustacea,  of  the  disappearance 
and  redevelopment  of  a limb  out  of  a rudiment  which  has  mean- 
while been  latent  (Mandibular  palp  of  the  Decapod  larva, 
Korschelt  and  Heider,  Vol.  II,  p.  312;  maxillipedes  of  the 
Stomatopoda,  Vol.  II,  p.  300.)  A similar  example  is  afforded 
among  the  insects  by  the  thoracic  limbs  of  many  Hymenoptera,” 
and  most  Diptera  for  that  matter.  "These  appear  as  rudiments 
in  the  embryo,  disappear  later,  and  reappear  in  the  imago.” 


116 


Armais  Entomological  Society  of  America  [VoL  XI, 


In  the  above-mentioned  resume  of  1899  Heymons  takes  up, 
point  by  point,  Verhoeff’s  work  on  Coleoptera  and  Hemiptera,  as 
well  as  his  papers  on  Traeheates  and  Myriapods  in  general,  all 
published  between  1892  and  1898.  From  the  results  of  his 
review  of  these  investigations  Heymons  concludes  that  there  is 
little  support  for  Verhoeff’s  opinions.  The  latter  include  the 
homology  of  the  styles  which  are  attached  to  the  coxae  of  the 
mesothoracic  and  metathoracic  legs  of  Machilis,  as  well  as  to 
certain  abdominal  somites  of  other  Thysanura.  According  to 
Heymons,  Verhoeff  compares  the  style-bearing  sclerites,  which 
he  considers  laterad  of,  and  fused  with,  the  true  abdominal 
sternites,  with  flattened  out  coxae,  and  that  rightly,  according 
to  Heymons;  but,  going  further  caudad,  Verhoeff  also  homol- 
ogizes  the  median  genital  appendages  with  the  distal  segments 
of  the  legs,  and  the  lateral  gonapophyses  with  the  coxae  of  these 
legs,  therefore  regarding  the  origin  of  two  pairs  of  genitalia 
from  one  pair  of  ambulatory  appendages  belonging  to  one 
somite,  instead  of  from  two  pairs  belonging  to  two  successive 
somites,  or,  to  put  it  from  Heymon’s  point  of  view,  from  at 
least  four  isolated  evaginations  having  no  connection  with  the 
anlages  of  the  segmental  appendages  found  in  the  embryo. 

One  objection  which  may  be  made  to  Heymons’s  theory,  on 
general  morphological  grounds,  is  found  in  certain  of  his  con- 
clusions which  he  himself  states  as  follows:  “Heymons  zufolge, 
sind  die  Geschlechtsanhange  mannlicher  und  weiblicher  Insekten 
nur  als  HypodermisfortsMze  zu  betrachten,”  and  “Die  Ge- 
schlechtsanhange sind,  nach  der  Ansicht  von  Haase,  Peytoreau, 
Heymons,  u.  a.  erst  innerhalb  der  Klasse  der  Insekten 
erworben.’’  With  but  few  exceptions  we  find  that,  in  tracing 
the  morphological  history  of  almost  any  organs  we  may  mention, 
more  or  less  important  and  well  developed  in  a group  of  animals, 
they  have  not  recently  “sprung  into  being’’  as  it  were.  Nature 
is  not  in  the  habit,  to  put  it  differently,  and  perhaps  in  a trite, 
old-fashioned  manner,  of  building  structures  out  of  “etwas 
Neues.’’  A glance  at  the  history  of  almost  any  vertebrate 
structure  will  reveal  an  example  of  this  fundamental  principle. 

Wheeler  realized  the  necessity  of  tracing  organs  not  only  in 
the  embryonic  stages,  but  also  on  through  later  ones.  In  his 
paper  on  Xiphidium  he  says  that  the  embryonic  history  of  the 
gonapophyses  could  be  “continuously  traced,’’  since  there  is  no 
flexure  of  the  abdomen  in  that  embryo  as  exists  in  so  many  other 


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117 


forms  to  obscure  the  ventral  view  of  the  somites.  After  the 
time  of  hatehing,  Wheeler  calls  attention  to  the  fact  that  Dewitz, 
in  1875,  traced  the  development  of  the  ovipositor  in  another 
loeustid,  Locusta  viridissima,  so  that  we  now  have  the  complete 
history  of  that  organ,  or  set  of  organs.  Wheeler  eoncluded  that 
part  of  his  account  as  follows:  ‘‘While  there  can  be  no  doubt 
about  the  appendages  of  the  eighth  and  ninth  segments  which 
go  to  form  the  two  outer  sheaths  of  the  ovipositor  or  sting,  the 
development  of  the  innermost  blades  is  by  no  means  so  satis- 
factory. But  whether  this  pair  is  only  a portion  of  the  ninth 
pair  of  appendages  as  most  authors  elaim,  or  represents  the 
tenth  pair  as  I maintain,  the  main  question  at  issue  is  in  no  wise 
affected;  for  it  still  remains  true  that  the  ovipositor  consists  of 
two  or  three  pairs  of  modified  ambulatory  limbs.”  In  the  male 
Xiphidium  embryo,  it  is  elaimed  by  Wheeler  that  the  pair  of 
appendages  on  the  ninth  somite  persists,  to  form  the  definitive 
styli,  those  of  the  eighth  and  tenth  somites  disappearing  very 
early.  To  quote  again,  “The  continuity  of  the  styli” — meaning 
here  male  genitalia — “with  the  embryonic  appendages  was 
quite  as  satisfactorily  observed  as  the  continuity  of  the  ovi- 
positor blades.”  He  also  says  of  the  investigations  of  others, 
“ Cholodkovsky  has  made  an  exactly  similar  observation  on 
Blatta.”  The  styli,  therefore,  in  the  male  “are  the  homologues 
of  the  second  pair  of  gonapophyses ” in  the  female.  “Haase 
must,  therefore,  have  gone  astray  in  seeking  to  homologize  the 
styli”  in  the  male,  “with  the  styloid  processes  or  ‘Griff el’” 
above-mentioned  in  this  paper  as  those  styles  attached  to  the 
coxae  of  certain  of  the  abdominal  somites  of  some  Thysanura, 
“for  the  styli,”  concludes  Wheeler  on  the  male  Xiphidium,  “are 
modified  ambulatory  appendages.” 

5.  Cerci. — One  more  pair  of  appendages,  namely,  the  cerei, 
should  properly  be  included  under  the  term  genitalia,  making 
the  total  number  four  pairs.  The  cerci,  often  tactile  in  funetion 
when  present,  are  frequently  described  as  attaehed  to  the  ter- 
minal or  anal  somite.  That  different  investigators  have  not 
meant  the  same  thing,  morphologically,  by  cerci,  is  undoubtedly 
true.  Some  regard  them,  not  as  appendages,  but  as  prolonga- 
tions of  pleurites,  i.  e.,  of  epimerites  and  episternites.  Berlese 
explains  this  point  of  view,  which  he  apparently  takes.  He  says 
that  there  may  be  eerei  on  the  tenth  somite,  as  also  on  the  ninth, 
the  presence  of  the  one  generally  excluding  that  of  the  other, 


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Annals  Entomological  Society  of  America  [Vol.  XI, 


although  he  would  not  lay  this  down  as  a fundamental  principle. 
He  gives  Notonecta  as  an  example  of  a case  where  he  maintains 
that  there  is  one  pair  of  cerci  on  the  eleventh  somite,  another 
pair  on  the  ninth,  and  on  somites  cephalad  of  these  he  thinks 
there  may  be  rudiments  of  others.  His  classification  of  cerci 
is  as  follows:  the  ones  found  on  the  eleventh  somite,  he  calls 
acrocerci,  or  cerci;  those  on  the  tenth,  mesocerci;  and  those  on 
the  ninth,  procerci.  The  views  of  other  authors  are  few  in 
number,  and  have  many  points  in  common.  Haase  considers 
them  as  feeler-like  appendages  of  the  ''Analstiick” ; Verhoeff, 
true,  segmental  appendages  of  the  tenth  abdominal  somite; 
Peytoureau,  dorsal  appendages  of  the  tenth  abdominal  somite 
which  may  be  compared,  he  thinks,  with  wings  in  their  method 
of  development. 

Heymons  and  Wheeler  in  Orthoptera,  and  Heymons  in 
regard  to  Dermaptera,  Ephemerida,  Odonata,  and  Thysanura 
agree  that  cerci  are  true  appendages  of  the  eleventh  abdominal 
somite. 

All  of  the  foregoing  opinions  except  Heymons’s  may  be 
grouped  together  in  that  all  their  authors  agree  that  the  cerci 
are  appendages,  of  one  kind  or  another,  belonging  to  the  ter- 
minal abdominal  somite.  Heymons  always  regards  the  ter- 
minal anal  somite  as  the  telson,  or  twelfth  abdominal  somite, 
so  would  regard  the  cerci  as  appendages  of  the  eleventh,  or 
pre-anal  somite.  Verhoeff  lays  great  stress  on  the  fact  that  the 
cerci  must  be  segmented  to  be  true  cerci,  comparing  their 
segmentation  with  that  of  the  thoracic  legs.  Haase  and  Hey- 
mons maintain  that  there  is  no  relationship  between  the  seg- 
ments of  these  two  structures  as  such,  but  rather  a far-reaching, 
“ weitgehende,”  according  to  Heymons — parallel  between  the 
cerci  and  the  antennae,  not  only  in  their  present  form,  but  in 
their  ontogeny.  It  is  certainly  true  that  the  cerci,  generally 
speaking,  bear  a superficial  resemblance  to  the  antennae,  but 
they  may  also  assume,  physiologically,  entirely  different  roles. 
Thus,  for  example,  they  may  be  purely  sensory,  but  they  may 
also  be  modified  as  accessory  copulatory  organs. 

Cholodkovsky  was  the  first,  in  1891,  to  uphold  the  fact  that 
the  cerci  were  morphologically  true  pedal  extremities,  and  it  is 
the  one  place  where  Heymons  can  agree  with  him,  as  well  as 
with  Wheeler  and  others,  that  a pair  of  appendages  which  may 
properly  be  included  under  the  genitalia  has  its  origin  in  the 


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anlages  of  the  appendages  of  an  embryonic  somite.  In  fact, 
Heymons  has  called  the  cerci  “modifizierte  Extremitaten,”  and 
he  states  very  emphatically  that  the  cerci  are  homologues  of  the 
above-mentioned  styles  of  some  Thysanura,  just  as  those  styles 
themselves  are  descended  from  ancestral  abdominal  appendages. 

6.  Acknowledgments. — It  is  with  the  foregoing  points 
of  theoretical  importance  in  mind  that  the  following  investiga- 
tion is  presented.  At  this  point  it  would  seem  fitting  to  state 
that  the  investigation  was  begun  at  the  suggestion  of  Dr.  Alex. 
D.  MacGillivray,  of  the  Department  of  Entomology,  University 
of  Illinois,  and  I wish  to  express  my  gratitude  to  him  for  that 
and  for  countless  timely  suggestions  and  criticisms.  I am 
indebted  to  Professor  S.  A.  Forbes  for  many  courtesies  and  for 
the  use  of  material  from  the  Illinois  State  Laboratory  of  Natural 
History,  and  also  to  the  staff  of  that  institution.  I also  desire 
to  thank  Dr.  Harris  H.  Wilder,  of  the  Department  of  Zoology 
of  Smith  College,  for  many  important  suggestions  and  criticisms. 
Dr.  H.  S.  Pratt,  of  the  Department  of  Zoology  of  Haverford 
College,  very  kindly  collected  for  me  specimens  of  Mantis  sp. 
from  a colony  introduced  on  nursery  stock,  near  Haverford,  and 
I would  at  this  point  express  to  him  my  thanks.  For  consid- 
erable mechanical  help  with  the  drawings  and  their  arrangement 
in  the  plates,  I am  very  grateful  to  Miss  N.  B.  Lewis,  of  Smith 
College. 

7.  Material. — The  records  upon  which  we  must  rely  in 
determining  the  origin  of  the  genitalia  are  the  anatomy  of 
generalized  adult  forms,  a comparison  of  these  with  more 
specialized  species  and  earlier  developmental  stages.  Therefore, 
this  paper  consists  of  a comparative  study  of  the  caudal  seg- 
ments and  appendages  of  adults  of  the  following  species : 
Lepisma  saccharina  and  Machilis  sp.  of  the  Thysanura;  Peri- 
planeta  orientalis,  Melanoplus  differentialis,  Dissosteira  Carolina, 
Xiphidium  ensiferum  and  Gryllns  pennsylvanicus  of  the  Orthop- 
tera;  Tihicen  septemdecim,  Notonecta  undulata,  Benacus  griseus, 
Corixa  sp.,  Anasa  tristis  and  Euschistus  variolarius  of  the 
Hemiptera;  Corydalis  cornuta  of  the  Neuroptera;  Panorpa 
lugubris  of  the  Mecoptera;  Nerophilus  calif ornicus  of  the 
Trichoptera;  Harpalus  caliginosus,  Cyhister  fimhriolatus , Hydro- 
philus  triangularis  and  Doryphora  decemlineata  of  the  Coleop- 
tera;  Hepialus  humuli,  Prionoxystus  rohinice,  Agrotis  ypsilon, 
Anosia  plexippus  and  Phlegethontius  sexta  of  the  Lepidoptera; 


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Annals  Entomological  Society  of  America  [Vol.  XI, 


Tipula  ahdominalis,  Tabanus  sulcifrons  and  Calliphora  viri- 
descens  of  the  Diptera;  and  of  the  Hymenoptera,  Dolerus 
unicolor  and  Vespa  maculata. 

II.  INVESTIGATION. 

General  Principles. — Before  taking  up  any  anatomical 
description  or  comparison  of  the  foregoing  forms,  a number  of 
preliminary  points  should  be  mentioned. 

The  distal  pair  of  appendages,  as  has  before  been  noted,  is 
the  cerci,  and  in  the  majority  of  cases  in  adult  insects  where 
these  are  present  they  have  so  changed  their  position  as  to  be 
dorso-lateral,  or  even  quite  dorsal.  As  many  of  the  succeeding 
pairs  of  appendages  as  are  present  are,  as  a rule,  still  in  a ventral 
position,  and  may  project  beyond  the  caudal  end  of  the  abdo- 
men. Therefore,  it  will  usually  seem  convenient  to  begin 
descriptions  of  the  genitalia  by  describing  the  cerci  first. 

Of  the  two  sexes  the  female  is  the  more  generalized.  A good 
example  of  this  point  is  seen  in  the  female  cockroach  where  all 
four  pairs  of  genital  appendages  are  present,  almost  in  their 
primitive  position  so  far  as  showing  their  points  of  attachment 
to  their  respective  segments  is  concerned,  and  where  the  total 
number  of  segments  found  in  adult  insects  is  also  present.  The 
saw-fly  is  another  striking  example  of  the  generalized  female. 
These  are  both  examples  in  primitive  families  of  insects,  but  on 
the  other  hand,  in  certain  specialized  groups  which  do  not  sting, 
and  which,  laying  their  eggs  merely  on  the  flat  surfaces  of  leaves 
or  stems,  lack  ovipositors,  the  caudal  end  of  the  abdomen  pre- 
sents a most  generalized  condition,  the  appendages  in  such 
cases  being,  ‘‘specialized  by  reduction.”  The  genital  and  anal 
openings  in  these  insects  may  be  easily  seen  in  a caudal  view, 
the  former  between  the  ninth  and  tenth  sternites  under  the 
edge  of  the  ninth,  and  the  anus  in  its  usual  position  between 
the  distal  tergite  and  its  corresponding  sternite.  These  openings 
and  whatever  rudimentary  appendages  there  may  be  present 
are  enclosed  within  a cavity  formed  by  the  invagination  of  the 
segments  beyond  and  including  the  eighth.  From  this  sac-like 
invagination,  the  appendages  may  be  protruded.  When  ovi- 
positors and  stings  are  present  in  specialized  forms,  these  too 
are  often  concealed,  or  at  least  partially  so,  in  pocket-like 
cavities  similar  to  the  one  described  above,  except  that  they  are 
usually  somewhat  longer. 


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121 


The  genital  opening  of  the  male  is  connected  with  the  tenth 
sternite  more  closely  than  with  any  other,  as  Berlese  states. 
However,  certainly  in  the  adult  insect,  it  is  also  situated  at  the 
distal  end  of  an  intromittent  organ,  which  is,  in  many  cases 
when  entirely  protruded,  nearly  as  long  as  the  abdomen,  and 
thus  the  ejaculatory  duct  is  also  prolonged  to  an  equally  great 
length,  therefore,  bringing  the  external  opening  itself  to  a point 
without  any  relation  to  the  abdominal  sclerites. 

Somewhat  similar  cases  occur  in  such  females  as  possess  long 
ovipositors.  However,  the  distal  opening  of  the  vagina  itself  is 
seldom  situated  far  beyond  the  bases  of  the  ovipositors.  When 
the  eggs  leave  this  opening,  they  follow  along  well-marked 
grooves  on  the  inner  surfaces  of  the  ovipositors  into  the  ground, 
stem,  or  other  object  in  which  they  are  to  be  laid.  This  same 
mechanism  may  exist  for  the  exit  of  poisonous  fluids  exuded  at 
the  bases  of  stings,  or,  as  is  often  the  case,  through  excurrent 
ducts  leading  from  the  glands  to  an  external  opening,  or  paired 
openings,  also  situated  at  the  bases  of  the  stings. 

In  those  insects  which  have  their  caudal  segments  and  gen- 
italia retracted,  the  caudal  end  of  the  body  has  a smoothly 
rounded  contour,  or  it  may  even  be  pointed.  Excellent  exam- 
ples of  such  cases  are  seen  in  the  Diptera  and  Hymenoptera. 
In  these,  one  is  unable  to  identify  the  sex  from  the  genitalia 
unless  they  are  extruded,  but  one  must  instead  use  other  char- 
acteristics varying  in  the  two  sexes — those  commonly  called 
secondary  sexual  characters.  Those  abdomens  which  terminate 
with  most  of  their  distal  segments  and  appendages  in  view, 
show  projections  of  a tactile,  clasping,  or  other  function,  and, 
although  usually  bilateral  in  arrangement,  they  are  very  irreg- 
ular in  appearance  by  contrast  with  those  smooth  forms 
described  above.  Here,  of  course,  it  is  very  often  possible  to  tell 
the  sex  easily  from  the  genitalia  alone. 

The  anus  is  always  surrounded  by  cuticular  membrane 
divided  into  folds  generally  called  anal  lobes.  It  is  often  difficult 
to  decide  upon  the  number  of  the  distal  segment  in  adult  insects 
because  it  cannot  be  differentiated  from  this  membrane  which 
may  very  well  be  made  up,  morphologically,  of  more  than 
one  segment. 

In  numbering  the  segments  of  this  region  it  is  not  necessary 
to  begin  with  the  first  abdominal  one.  The  most  caudal  pair  of 


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Annals  Entomological  Society  of  America  [Vol.  XI, 


abdominal  spiracles  typically  occurs  in  the  eighth  abdominal 
segment  of  adult  insects,  but  is  sometimes  concealed  if  the 
posterior  segments  are  retracted;  otherwise,  it  is  in  the  seventh, 
and  the  arrangement  in  this  partieular  is  quite  uniform  through- 
out an  order.  As,  for  example,  there  are  always  eight  pairs  of 
abdominal  spiraeles  in  the  Orthoptera  but  only  seven  pairs  in 
the  Lepidoptera,  with  the  possible  exeeption  of  Hepialus.  The 
faet  must  not  be  lost  sight  of  that  in  the  larva  of  this  form 
eight  pairs  of  functional  spiracles  are  present,  and  that  these  are 
rudimentary  in  the  pupa.  The  caudal  appendages  of  the 
abdomen,  the  genitalia,  are  designated  in  this  paper  by  the 
Roman  numerals  I,  II,  III  and  IV,  beginning  with  the  eephalic 
pair.  No  attempt  has  been  made  to  apply  the  names  given  by 
systematists  to  these  parts. 

With  the  foregoing  general  principles  in  mind,  some  aceount 
of  the  details  of  the  work  may  now  properly  be  considered. 

Method  of  Preparation. — The  method  of  preparing 
inseets  for  a study  such  as  the  following  is  very  simple.  They 
were  softened  by  leaving  the  entire  inseet,  the  abdomen  only, 
or  merely  the  posterior  end,  whichever  was  desired,  in  a five 
per  eent  solution  of  caustic  potash  for  periods  varying  from 
twelve  to  twenty-four  or  thirty-six  hours,  depending  upon  the 
hardness  and  freshness  of  the  specimens  used.  If  pinned 
speeimens  were  used,  they  were  first  boiled  in  water  for  a short 
time.  They  were  then  washed  in  running  water,  and  studied 
under  a binoeular  dissecting  microscope.  A compound  micro- 
scope was  also  used  for  studying  mounted  balsam  preparations 
of  the  smaller  parts. 

Discussion  and  Tables. — The  arrangement  of  this  section 
of  the  paper  will  be  as  follows : The  Apterygota  will  be  taken  up 
first,  and  next  the  Pterygota,  beginning  in  each  case  with  the 
generalized  forms.  There  are  also  included  tables  showing  the 
sclerites  and  appendages  present  in  the  species  studied.  The 
presenee  of  a selerite  or  a pair  of  appendages  is  indicated  in  the 
tables  by  a plus  sign,  and  their  absence  by  a minus  sign.  When 
either  is  rudimentary,  an  asterisk  is  added  to  the  plus  sign.  The 
abbreviations  t and  s stand  for  tergum  and  sternum  respectively. 

a.  Thysanura. — It  is  obvious  from  the  figures  of  both 
Lepisma  and  Machilis  that  the  problem  is  eomplicated  in  the 
Thysanura  rather  than  simplified,  as  would  seem  natural.  . It  is 


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123 


here  that  Heymons  makes  his  best  point  in  regard  to  the 
homologies  between  styles  and  genitalia,  but  in  these  forms 
both  styles  and  appendages  are  often  attached  to  the  same 
somites.  A careful  survey,  however,  of  Figure  12  (Plate  IV)  of 
the  more  generalized  female  shows  that  the  latter  are  important 
outgrowths,  which  so  far  as  the  adults  are  concerned,  may  far 
better  be  considered  genitalia  than  styles.  In  the  embryos 
figured  by  Heymons  the  buds,  anlages  of  genitalia  and  styles, 
are  so  near  together  as  to  be  easily  confused  and  to  give  ground 
for  the  belief  that  they  are  one  and  the  same  thing,  not  separate 
from  the  very  beginning.  On  the  other  hand,  this  separation 
shows  very  clearly  in  his  figures,  even  in  those  of  insects  which 
have  entirely  degenerate  styles;  that  is,  none,  in  the  adult.  He, 
however,  does  not  interpret  his  figures  nor  yet  his  material  in 
that  way.  He  considers  that  the  appendages  found  in  the  adult 
are  simply  the  final  specialization  of  these  same  above- 
mentioned  styles. 

In  the  male  and  female  Lepisma  (Plate  IV,  Figs.  6,  7,  10,  and 
12),  again  it  is  evident  that  in  the  adult  insect  there  are  appen- 
dages corresponding  to  Appendage  I as  well  as  styles,  on  the 
same  somite,  and  it  seems  unnecessary  to  correlate  those 
appendages  found  on  the  terminal  somite  of  Lepisma  and 
Machilis  with  styles  when  they  resemble  so  closely  certain 
appendages,  cerci  or  Appendage  IV,  of  similar  form  in  many 
groups  where  styles  are  not  present.  It  should  be  said  in  this 
connection  that  the  terminal  median  appendage  present  in  the 
Lepisma  and  shown  in  the  figures  of  that  insect  is  the  one 
which,  including  also  the  anal  lobes,  Heymons  and  Uzel 
homologize  with  the  eleventh  somite. 


Table  of  Sclerites  and  Appendages. 


Lepisma  saccharina  7, 

Female t-j- 

s-j- 

Male t-t- 

s-j- 

Machilis  sp. 

Female t+ 

s-j- 

Male t-h 

s+ 


SOMITES 

APPENDAGES 

8, 

9, 

10, 

11, 

I, 

n, 

III, 

IV. 

t+ 

t+ 

t+ 

t-h 

+ 

+ 

+ ? 

+ 

s-F 

s-F 

S+ 

s-h 

t-|- 

t+ 

t-h 

t-f- 

+ 

+ 

+ ? 

+ 

S-F 

s+ 

s-h 

s-h 

t+ 

t+ 

t+ 

t+ 

+ 

— 

— 

+ 

S+ 

S+ 

s+ 

s+ 

t+ 

t+ 

t-t 

t-f- 

+ 

+ 

+ ? 

+ 

s-F- 

S-f- 

S-t- 

S+ 

124 


Annals  Entomological  Society  of  America  [Vol.  XI, 


h.  Orthoptera. — In  regard  to  the  Orthoptera  it  may  be  said 
that  they  are  of  course  here,  as  elsewhere  in  structure,  a very 
generalized  group.  To  begin  with,  the  tables  show  the  presence 
of  eleven,  or  at  least  parts  of  ten,  somites  and  all  four  pairs  of 
appendages  in  all  the  forms  studied.  This  is  particularly 
remarkable  in  connection  with  Appendage  II,  the  commonly 
called  “mesal,”  or  “median”  pair  of  appendages,  which  are  so 
many  times  entirely  lacking  in  the  female. 

In  no  case  is  the  latter  pair  so  prominent  in  the  above  men- 
tioned genera  as  in  Mantis.  However,  in  case  of  every  mod- 
ification of  the  genitalia,  whether  it  be  for  the  purpose  of  digging 
in  the  ground,  as  is  true  in  the  grasshopper  and  the  cricket,  or 
whether  for  holding  the  spermatophore,  the  habit  of  the  female 
Xiphidium,  it  is  possible  easily,  not  only  to  work  out  and  see 
plainly  this  appendage,  Appendage  II,  but  also  to  see  that  it 
follows  immediately  upon  Appendage  I in  an  extreme  ventro- 
caudal  position. 


Table  of  Sclerites  and  Appendages. 


SOMITES 

APPENDAGES 

Periplaneta  orientalis 

7, 

8, 

9, 

10, 

11 

I, 

n, 

III, 

IV. 

Female 

t-h 

t-h 

t-h 

t-h 

-h 

-h 

-F 

+ 

s+-f-s-|- 

s+ 

s-h 

s-h 

Male 

t-h 

t-h 

t-h 

t-h 

-h 

-h 

-h 

S+ 

s+ 

s-h 

s-h 

s-h 

Melanoplus  differentialis 

Female 

t-h 

t+ 

t-h 

t+ 

t-h 

-h 

+ 

-h 

S-h 

s-h 

s+ 

s-h 

s-h 

Male 

t-l- 

t-h 

t-h 

t-h 

t-h 

-h 

-h 

+ 

+ 

s-h 

s+ 

s-h 

s-h 

s-h 

Dissosteira  Carolina 

Female 

t-h 

t-h 

t-h 

t-h 

t-h 

-h 

+ 

-h 

-h 

• 

s-h 

s-h 

s-h 

s-h 

Male ; 

t-h 

t-h 

t-h 

t-h 

t-h 

-h 

-h 

-h 

-h 

s-h 

s-h 

s-h 

s-h 

s-h 

Xiphidium 

Female 

t-h 

t-h 

t-h 

t-h 

t-h 

-h 

-h 

-h 

-h 

s-h 

s-h 

s+ 

s-h 

s-h 

Male 

t+ 

t+ 

t-h 

t-h 

t-h 

+ 

-h 

-h 

-h 

s-h 

s-h 

s-h 

s-h 

s-h 

Gryllus 

Female 

t+ 

t-h 

t-h 

t-h 

+ 

+ 

-h 

-h 

s-h 

S+ 

s-h 

s-h 

s+ 

Male 

t-h 

t-h 

t+ 

t + 

t-h 

-h 

+ 

+ 

-h 

s+ 

s+ 

s-h 

s-h 

s-h 

1917] 


Morphology  of  Genitalia  of  Insects 


125 


c.  Hemiptera. — In  many  species  of  this  order  we  meet  the 
problem  presented  by  Berlese’s  theory  of  successive  pairs  of 
cerci,  which  he  illustrated  by  many  examples  from  the  Hemip- 
tera. At  the  posterior  end  of  Benacus,  Zaitha  and  other  species 
of  aquatic  Hemiptera,  in  both  the  male  and  female  there  pro- 
jects a pair  of  strap-like  appendages,  included  by  some  authors 
among  the  genitalia.  Upon  a close  examination  they  are  found 
to  be  outgrowths  of  the  eighth  tergites,  and  the.  corresponding 
pair  of  spiracles  is  situated  at  their  bases.  From  these  spiracles 
two  parallel  rows  of  closely  set  setae  extend  to  the  distal  ends  of 
these  projecting  tergites.  Various  observers  have  believed 
them  to  be  organs  used  in  connection  with  the  respiration  of 
these  aquatic  species.  The  seventh  tergite  of  Benacus  presents 
a similar  modification,  and  it  contains  the  seventh  pair  of  spir- 
acles, but  it  is  much  broader  and  shorter.  The  seventh  and 
eighth  tergites  of  Notonecta  and  the  eighth  tergite  of  Corixa 
are  apparently  lengthened  in  like  manner,  and,  according  to 
some  investigators,  have  also  a like  function.  Euschistus 
variolarius  and  Anasa  tristis,  among  the  land  forms,  show  similar 
projections  from  the  tergites  of  this  region,  but  lack  the  arrange- 
ments of  setae  which  have  to  do  with  the  respiration  of  the 
aquatic  species.  However,  in  neither  case  are  these  parts  sep- 
arated from  the  sclerite  proper,  as  is  always  true  of  the  cerci, 
whether  or  not  they  show  segmentation.  In  this  connection, 
it  may  be  noted  that  these  prolongations  in  the  Hemiptera, 
called  by  Berlese  the  cerci,  are  never  segmented.  The  Hemip- 
tera form  a generalized  order  of  insects,  yet  they  are  among  the 
most  specialized  of  those  having  an  incomplete  metamorphosis. 

There  are,  therefore,  few  appendages  present  in  certain  of 
the  more  highly  developed  species,  as  is  evident  from  the  fol- 
lowing table,  and  they  are  also  specialized  by  modification  in  the 
form  of  complicated  mechanisims.  Examples  of  the  latter  are 
seen  in  the  males  of  both  Euschistus  and  Anasa. 


126 


Annals  Entomological  Society  of  America  [Vol.  XI, 


Table  of  Sclerites  and  Appendages. 


Tibicen  septemdecim  7, 

Female t+ 

5 + 

Male t+ 

Notonecta  imdulata 

Female t+ 

s+ 

Male t+ 

s+ 

Benacus  grisens 

Female t+ 

s+ 

Male t+ 

s+ 

Corixa  sp. 

Female t4- 

s-j- 

Anasa  tristis 

Female t+ 

s+ 

Male t+ 

s-[- 

Euschistus  variolar  ins 

Female t+ 

s-j- 

Male t+ 

s+ 


SOMITES  APPENDAGES 


8, 

9, 

10, 

11 

h 

n. 

III, 

IV. 

t+ 

t+ 

tF 

F 

F 

F 

F 

s+ 

sF 

sF 

t+ 

tF 

tF 

F 

F 

F 

F 

t+ 

tF 

tF 

t— 

F 

F 

F 



S+ 

sF 

sF 

s — 

t+ 

tF 

tF 

t— 

F 

F 

F 

— 

S+ 

sF 

sF 

t— 

t+ 

tF 

tF 

t — 

F 

— 

F 

— 

S+ 

sF 

sF 

t— 

t + 

tF 

tF 

t— 

F 

F 

F 

— 

S+ 

sF 

sF 

t — 

t+ 

tF 

tF 

t— 

F* 

— 

— 

— 

S+ 

sF 

sF 

s — 

t+ 

tF 

tF 

tF 

F* 

F* 

F* 

— 

S+ 

sF 

sF 

sF 

t+ 

tF 

tF 

t— 

F 

F 

F 

— 

S+ 

sF 

sF 

s — 

t + 

tF 

tF 

t— 

F* 

— 

— 

— 

S+ 

sF 

sF 

s — 

t+ 

tF 

tF 

t — 

F 

F 

F 

— 

S+ 

sF 

sF 

s — 

d.  Neuroptera. — Here  again,  among  the  first  of  those  forms 
characterized  by  a complete  metamorphosis,  we  find  a more 
generalized  condition  than  among  the  Hemiptera,  which, 
although  they  have  an  incomplete  metamorphosis,  stand  at  the 
top  of  the  group.  Appendage  II  is  lacking,  but  this  is  the  above- 
mentioned  “mesal”  appendage  more  often  absent  than  present. 

To  be  sure,  somite  eleven  is  apparently  entirely  wanting,  but 
without  embryological  evidence  one  has  always  a suspicion  that 
parts  of  this  segment  may  be  present  in  the  membrane  of  the 
anal  lobes.  Another  point  to  be  noted  here,  unlike  any  we  found 
in  the  Orthoptera,  is  that  the  male  appendages  present  almost 
as  primitive  a condition  as  do  the  female.  In  fact  there  is  even 
less  specialization  in  connection  with  function  in  the  male  than 
in  the  female. 


Table  of  Sclerites  and  Appendages. 

SOMITES 

Corydalis  cornuta  7,  8,  9,  10,  11 

Female t-j-  t-j-  t-t-  t-l-  t — 

s-j-  s-j-  s-j-  S-j-  s — 

t-j-  t-f-  tT  t-f-  t — 

s-j-  s-j-  s-j-  s-F  s — 


APPENDAGES 

I,  II,  III,  IV. 
+ • - + + 

+ — 


Male 


+ + 


1918] 


Morphology  of  Genitalia  of  Insects 


127 


e.  Mecoptera. — Panorpa  luguhris,  the  example  ehosen  in  this 
case,  seems  at  first  glance  to  be  a most  specialized  insect,  par- 
ticularly so  far  as  genitalia  are  concerned.  This  appearance  is 
found  to  be,  with  very  little  and  superficial  examination, 
entirely  misleading.  The  real  situation  at  the  posterior  ends  of 
both  the  male  and  female  Panorpa  is  that  of  a generalized  form. 
In  the  male  there  is  a resemblance  to  the  Lepidoptera  in  the 
claspers,  which  are  not,  however,  the  only  appendages  present 
as  is  usually  the  case  in  the  larger  group  characterized  by  such 
organs. 

Table  of  Sclerites  and  Appendages. 


SOMITES  APPENDAGES 

Panorpa  lugubris  7,  8,  9,  10,  11  I,  II,  III,  IV. 

Female tT  t-j-  t-H  tT  tp  P — P P 

sP  sP  sp  sp  sp 

Male tp  tp  tp  tp  t — p — p p 

s-j-  sp  sp  s-j-  sP 


/.  Trichoptera.— The  male  caddis  fly  is  characterized  by  an 
apparent  specialization,  real  indeed  so  far  as  function  is  con- 
cerned but  not  fundamentally  affecting  the  relative  arrangement 
of  parts.  The  specialization  is  in  connection  with  the  pro- 
longation merely  of  the  ejaculatory  duct,  and  is  formed  of 
Appendage  II. 

Table  of  Sclerites  and  Appendages. 

SOMITES 

Nerophilus  calif ornicus  7,  8,  9,  10,  11 

Female 

Male tp  tp  tp  tp  tp* 

sp  sp  sp  sp  sP* 

g.  Coleoptera. — The  Coleoptera  have  long  presented  a great 
problem  to  those  investigators  who  wished  to  be  able  to  make  a 
classification  of  that  group  based  on  genitalia.  So  far  as  this 
paper  is  concerned  they  may  still  present  almost  unsurmount- 
able  difficulties.  However,  there  is  very  little  doubt  that  ten 
segments  and  even  traces  of  eleven  are  present  in  the  beetles, 
even  if  one  must  depend  in  large  measure  upon  membrane  only 
and  asymmetrically  placed  sclerites.  With  relaxation  by 
potash  it  is  very  evident  that  true  somites  eight,  nine,  and  ten 
are  present,  the  sutures  between  them  showing  plainly  by  means 
of  evaginated  folds  or  grooves.  The  eighth  somite  is  always 
indicated  plainly  by  the  position  of  the  eighth  spiracle,  no 


appendages 
I,  II,  III,  IV. 

P P P P 


128 


Annals  Entomological  Society  of  America  [Vol.  XI, 


matter  how  much  it  is  hidden  from  view  at  first  glance.  Appen- 
dages are  in  large  measure  lacking  in  the  female  and  the  appear- 
ance is  that  of  extreme  specialization  by  reduction.  The  male 
is  modified  especially  in  connection  with  the  external  opening 
of  the  ejaculatory  duct,  which  is  placed  at  some  distance 
outside  of  the  body-cavity,  entirely  out  of  relation  to  its 
respective  somites  9 and  10. 

Table  of  Sclerites  and  Appendages. 


SOMITES  appendages 


Harpahis  caliginosns 

7, 

8, 

9, 

10, 

11 

I, 

n, 

Ill, 

IV. 

Female 

t+ 

t-t 

t-|- 

t+ 

+ 

— 

— 

— 

s+ 

s+ 

S-h 

S+ 

s-f- 

Male 

t+ 

t+ 

t-f- 

t— 

— 

+ 

+ 

— 

s+ 

s-H 

S-f- 

S+ 

s — 

Cyhister  fimbriolatus 

Female 

t+ 

t-}- 

t-t- 

t+ 

+ 

+ 

— 

S+ 

S-1- 

S+ 

s4- 

S+ 

Male 

t-t- 

t+ 

t+ 

t— 

+ 

+ 

+ 

— 

S+ 

s-i- 

S+ 

S-h 

s — 

Hydrophilus  triangularis 

Female 

t+ 

t+ 

t+ 

t-F 

t— 

+ 

+ 

+ 

— 

S+ 

S-K 

S+ 

s+ 

s — 

Male 

t-l- 

t-l- 

t+ 

t— 

+ 

+ 

+ 

— 

s+ 

s-H 

S+ 

S+ 

s — 

Doryphora  decemlineata 

Female 

t+ 

t-1- 

t+ 

t— 

+* 

— 

— 

— 

S+ 

S+ 

s-H 

S-t- 

s — 

Male 

t+ 

t-1- 

t-l- 

t— 

+? 

+ 

— 

S+ 

S-I- 

s-f- 

s — 

s — 

h.  Lepidoptera . — The  families  of  Lepidoptera  present  in  the 
female,  beginning  with  Hepialus,  most  extreme  cases  of  special- 
ization by  reduction.  The  telescoping  of  segments  is  here 
carried  to  such  a degree  that  we  see  for  the  first  time  the  most 
terminal  spiracle  in  the  seventh  somite  instead  of  in  the  eighth, 
its  usual  position  in  a more  typical  form.  It  is  interesting  to 
note,  in  this  connection,  that  this  spiracle  is  present  in  the 
larva,  rudimentary  in  the  pupa,  and  lost  in  the  adult,  with  the 
possible  exception  of  Hepialus. 

The  somites  retracted  are  very  long  in  proportion  to  their 
width,  and  very  slightly  chitinized.  Appendages  in  the  female 
are  largely  lacking  except  perhaps  for  bud-like  outgrowths  from 
the  somites  at  the  positions  occupied  by  appendages  when 
present  in  other  forms.  The  appearance  of  the  female  from  the 
caudal  point  of  view  presents,  particularly  in  Hepialus,  because 
of  this  relation  between  somites  and  the  origins  of  their  respec- 


1918] 


Morphology  of  Genitalia  of  Insects 


129 


live  pairs  of  genitalia,  a most  generalized  condition.  The  use  of 
the  word  generalized  may  be  objected  to  in  a case  of  such 
extreme  specialization,  *but  certainly  the  relation  between 
somites  and  appendages  is  a primitive  characteristic  in  itself, 
and  one  extremely  prominent  in  this  group. 

Table  of  Sclerites  and  Appendages. 


Hepialus  humuli  7, 

Female t+ 

s+ 

Male t+ 

s-j- 

Pryonoxystus  robinicB 

Female t+ 

s+ 

Male t+ 

s+ 

A gratis  ypsilon 

Female t+ 

s+ 

Male t+ 

s-j- 

Anosia  plexippus 

Female t+ 

s+ 

Male t+ 

s-j- 

Phlegethontius  sexta 

Female t+ 

s+ 

Male t+ 

s+ 


SOMITES  APPENDAGES 


8, 

9, 

10, 

11 

I, 

11, 

III, 

IV. 

t+ 

t+ 

t+ 

t— 

-f* 

— 

— 

— 

s+ 

S+ 

S+ 

s — 

t+ 

t+ 

t+ 

t — 

+ 

— 

— 

— 

S-h 

S+ 

S+ 

s — 

t+ 

t+ 

t+ 

t+ 

— 

— 

— 

— 

S+ 

S+ 

S+ 

S+ 

t+ 

t+ 

t+ 

t+ 

-f 

-f 

-f 

• — 

S+ 

S+ 

S+ 

S+ 

t+ 

t+ 

t+ 

t+ 

— 

— 

— 

— 

S+ 

S+ 

S+ 

s-i- 

t+ 

t+ 

t+ 

t— 

-f 

-f 

+ 

— 

S+ 

S+ 

S+ 

s — 

t+ 

t+ 

t+ 

t— 

— 

— 

— 

— 

S+ 

S+ 

S+ 

s — 

t+ 

t+ 

t+ 

t— 

-f 

+ 

+ 

— 

S+ 

S+ 

S+ 

s — 

t+ 

t+ 

t+ 

t+ 

— 

— 

— 

— . 

S+ 

S+ 

S+ 

S-f-  , 

t+ 

t+ 

t+ 

t+ 

-f 

-f 

-f 

— 

S+ 

S+ 

S+ 

s-f 

i.  Diptera. — The  Diptera  differ  among  themselves  largely  in 
presenting  both  very  generalized  and  specialized  conditions. 
The  specialization,  so  far  as  appendages  is  concerned,  is  again 
one  of  reduction.  The  best  illustration  of  generalization  is  seen 
in  the  female  of  Tipula  ahdominalis  and  specialization  is  evident 
in  the  tabanid.  A caudal  view  (Plate  XVI)  illustrates  extreme 
specialization  by  reduction  with  scarcely  any  appendages  indi- 
cated except  the  cerci.  Appendage  IV.  In  this  as  well  as  in  all 
cases  of  this  type  of  specialization  both  the  anal  and  the  genital 
openings  occupy  their  typical  position.  The  male  shows  greater 
specialization  both  in  Appendage  IV  and  in  the  other  appen- 
dages, especially  in  the  one  forming  the  case  for  the  ejaculatory 
duct.  Appendage  II,  but  even  here,  comparatively  speaking, 
specialization  by  modification  and  enlargement  of  parts  is 
fairly  slight. 


130 


Annals  Entomological  Society  of  America  [Vol.  XI 


Table  of  Sclerites  and  Appendages. 


SOMITES  APPENDAGES 

Tipula  abdominalis  7,  8,  9,  10,  11  I,  II,  III,  IV. 

Female t+  t+  t+  t+  t — +?  — — + 

s+  s+  s+  s+  s — 

Alale tT  tT  tT  tT  t — T T T T 

s-j-  s+  s+  s+  s — 

Tabaniis  sulcifrons 

Female t+  t+  t+  t+  t — — — — — 

s+  s+  s+  s+  s — 

jVIale tT  tT  tT  tT  t — T T T T 

sT  sT  sT  sT  s — 

Calliphora  viridescens 

Female tT  tT  tT  tT  t — — — — — 

sT  sT  sT  sT  s — 

]VIale tT  tT  tT  tT  t — T*  T T T 

sT  sT  sT  sT  s — 


j.  Hymenoptera. — The  connections  of  the  8th  and  9th 
somites  with  their  respective  genitalia  are  very  clearly  seen, 
not  only  in  the  generalized  saw-fly,  Dolerus,  but  also  in  the 
specialized  Vespa  (Plate  XVII).  The  genitalia,  here  having  the 
form  of  saws  and  stings  respectively,  are  in  themselves  very 
naturally  greatly  modified  for  their  functions,  but,  except  for 
their  length  and  serrated  edges,  for  example,  there  is  very  little 
about  the  posterior  ends  of  the  females  of  either  of  the  above 
mentioned  genera  which  indicates  very  great  specialization. 
The  one  point  which  does  strongly  suggest  such  specialization 
is  the  complete  retraction  of  parts  in  this  region  of  the  body  so 
that  without  potash  preparations  one  would  see  only  a perfectly 
even  contour  in  the  caudal  region  of  the  abdomen. 

The  males  of  this  order  show  numerous  small  modifications 
of  all  the  genitalia,  Appendages  I,  II,  III,  and  IV  respectively. 
These  modifications  are  in  the  form  of  many  irregular  points, 
curved  projections,  finger-like  evaginations,  and  other  small 
structures  hard  to  describe.  The  copulatory  habits  of  these 
forms  have  been  worked  on  so  little  that  nothing  can  be  said 
with  regard  to  the  meaning  of  all  these  structures.  Their 
positions  in  relation  to  their  respective  segments  are  not  difficult 
to  make  out,  as  is  evident  from  the  plates  showing  figures  of 
these  forms. 


1918] 


Morphology  of  Genitalia  of  Insects 


131 


Table  of  Sclerites  and  Appendages. 

SOMITES  APPENDAGES 


Dolerus  unicolor 

7, 

8, 

9, 

10, 

11 

I, 

Ifi 

III, 

IV. 

Female 

t+ 

t+ 

t+ 

t+ 

t— 

+ 

+ 

+ 

+ 

s-t 

S+ 

s+ 

S-i- 

s — 

Male 

t+ 

t+ 

t+ 

t-f 

t— 

+ 

+ 

+ 

— 

S-h 

S+ 

S+ 

s-F 

s — 

Vespa  maculata 

Female 

t+ 

t+ 

t-f- 

t+ 

t— 

+ 

+ 

+ 

— 

S+ 

s-i- 

S+ 

s+ 

s — 

Male 

t+ 

t+ 

t+ 

t+ 

t— 

+ 

+ 

+ 

— 

S+ 

S+ 

S-t 

S+ 

S+ 

III.  SUMMARY. 

Comparisons  between  certain  of  the  somites  of  the  different 
orders  investigated,  as  well  as  between  some  of  the  appendages 
studied,  may  well  be  taken  up  as  a summary  of  the  above  dis- 
cussions and  tables.  The  homology  of  the  sclerites  of  the 
species  studied,  as  well  as  that  of  the  appendages,  has  been 
fully  and  clearly  indicated  in  the  labeling  of  the  figures. 

1.  Somite  Eight. — This  somite,  as  has  already  been  noted, 
contains,  typically,  the  terminal  pair  of  spiracles.  Except  in 
those  species  which  have  well-rounded  contours,  or  are  pointed, 
at  the  caudal  end  of  the  abdomen,  this  somite  approaches  very 
nearly  the  one  figured  in  the  so-called  primitive  type  (Plate  IV, 
Fig.  1).  It  is  simple  in  outline;  broad  and  blunt  in  shape; 
about  one-third  as  long  as  wide;  tapering  only  very  slightly,  if 
at  all,  and  with  a tergum  and  sternum  almost  equal  in  size,  con- 
nected laterally  by  an  appreciable  conjunctiva;  in  the  Thysa- 
nura,  Orthoptera,  Hemiptera,  and  in  the  generalized  orders 
studied  having  a complete  metamorphosis,  such  as  the  Neurop- 
tera,  Mecoptera,  and  Trichoptera.  In  the  Coleoptera  and 
Lepidoptera  it  is  retracted;  more  or  less  membranous;  long  in 
proportion  to  its  width;  and,  in  the  Lepidoptera,  except  for  the 
possible  case  of  Hepialus,  it  lacks  its  respective  spiracle.  It  is 
also  small  in  the  higher  families  of  the  Diptera,  but  its  extreme 
specialization  occurs  in  the  female  Hymenoptera  where  the 
sternum  consists  of  two  small,  sub-triangular  sclerites  to  which 
is  attached  its  respective  pair  of  appendages,  I,  saws  or  sting  as 
the  case  may  be.  (Plate  XVII,  Figs.  10  and  14). 

2.  Somite  Nine. — This  somite  is  more  specialized  than  the 
eighth  and  markedly  shorter  in  proportion  to  its  width  even  in 
the  Thysanura  and  Orthoptera.  In  these  generalized  orders  of 


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insects,  with  incomplete  metamorphosis,  the  ninth  somite  shows 
specialization  in  the  sterum,  which,  early  in  its  history  in  the 
female  cockroach  and  grasshopper,  is  much  smaller  and  far 
more  variable  in  shape  than  the  tergum.  In  the  Hemiptera  it  is 
a larger,  less  modified  somite,  in  the  sternum  as  well  as  in  the 
tergum,  and  this  continues  to  be  true  in  Corydalis  and  Panorpa, 
although  it  is  longer  in  proportion  to  its  width  than  before,  this 
latter  characteristic  following  out  the  general  shape  of  the 
scorpion  fly.  In  the  Coleoptera  the  entire  somite  consists  of 
most  irregularly  shaped  chitinous  sclerites,  and,  in  large  pro- 
portion, of  cuticular,  non-chitinized  membrane.  Such  sclerites 
may  not  be  bilaterally  placed  with  reference  to  the  shape  of  the 
beetle,  but  in  a direct  ventral  view  only  a part  of  the  sternum 
will  show,  and  that,  irregular  in  shape,  as  in  Hydrophilus 
(Plate  XIII).  In  the  Lepidoptera  the  ninth  somite  is  often  a 
homogeneous,  membranous  cylinder  as  in  the  females  of 
Phlegethontius  and  Pryonoxyatus ; or,  as  in  the  male  of  the 
same  genus  there  may  be  a slender,  curved  sclerite  bilaterally 
placed  in  a broad  area  of  membrane;  or,  as  is  true  of  Hepialus 
the  sclerites  may  be  broad  and  short,  more  highly  chitinized 
than  the  succeeding  somites.  In  the  Diptera  it  varies  from  the 
small,  crescent-shaped  sternum  of  the  female  Tipula  abdom- 
malis,  to  the  broad,  well-rounded  tergum  of  the  male  in  the 
same  species. 

Between  these  two  extremes,  one  finds  every  irregularity,  of 
size  and  shape,  as  is  well  illustrated  by  the  long,  sub-cylindrical 
somite  of  the  male  blow-fly  and  the  irregularly  chitinized, 
largely  membranous  sternum  of  the  female  of  the  tabanid.  The 
corresponding  sclerite  in  the  male  further  accentuates  the  shape 
found  in  the  female  so  that  it  is  almost  forked,  the  points  pro- 
jecting posteriorly  and,  in  the  female  blow-fly  we  meet  with  an 
almost  typical  ninth  sternum,  its  only  variation  being  a some- 
what curved  caudal  margin. 

The  ninth  sternum  is  highly  specialized  in  shape  and  arrange- 
ment in  the  Hymenoptera,  after  the  same  manner  already  com- 
mented upon  in  connection  with  the  eighth,  and  it  consists  of 
two  irregular  sclerites  again  somewhat  approaching  a triangular 
shape.  However,  just  as  plainly  marked  as  in  the  case  of  the 
eighth,  is  the  primitive  connection  of  this  sternite  with  its 
respective  pair  of  appendages:  a most  generalized  point  in  a 
highly  specialized  group.  It  should  also  be  noted  that  this 


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133 


generalized  eondition  is  almost  as  clearly  seen  in  Vespa  as  in 
the  saw-fly. 

3.  Somite  Ten. — The  typical  form  of  this  somite  holds 
good,  for  the  tergum  in  the  male  and  female  Lepisma,  the 
sternum  in  these  forms  having  as  its  main  characteristic  a deep 
indentation  in  the  middle  of  the  caudal  margin.  In  the  grass- 
hoppers this  tergum  is  narrow  and  only  partly  divided  from  the 
ninth  by  an  incomplete  suture,  in  both  male  and  female,  but 
the  sternum  is  nearly  typical.  In  the  female  cockroach  it  is  so 
deeply  indented  in  the  middle  of  the  caudal  margin  as  to  seem 
almost  forked,  and  in  the  male  this  sclerite  is  very  short  with 
an  entire,  caudal  margin,  while  the  sternum  is  very  small  and 
retracted  in  both  cases.  In  the  male  and  female  crickets  the 
tergum  is  a sclerite  nearly  as  long  as  broad,  with  a well-rounded 
caudal  margin,  but  the  sternum  is  smaller,  much  shorter  than 
broad,  and  indented  on  the  caudal  margin,  as  is  also  the  tergum 
of  the  female  Xiphidium.  The  sternum  again  in  this  genus,  as 
in  all  of  the  Orthoptera  studied,  shows  specialization  to  a slight 
degree  in  its  being  retracted  under  the  preceding  sterna  and 
terga  with  a consequent  reduction  in  size.  In  the  Hemiptera 
this  small  size  of  somite  ten,  with  its  accompanying  retraction, 
is  carried  'to  a greater  extent,  and  we  have  small  sclerites,  still 
chitinized,  and,  for  all  those  studied,  very  well  illustrated  by  the 
terminal  tergum  of  Benacus  which  is  typical  of  such  sclerites, 
well  developed,  considering  that  they  are  retracted.  The  latter 
point  is  clear  when  such  a tergum  is  compared  with  the  tenth 
tergum  or  sternum  of  Euschistus.  In  all  the  Hemiptera  studied 
there  was  quite  perceptible  chitinization  of  the  cuticula  forming 
the  tenth  somite,  but  this  is  lacking  in  the  Neuroptera  where 
membrane  only  is  present.  The  somite  in  this  case  is  not  only 
short,  but  also  small  in  circumference,  entirely  covered  by  other 
somites  and  appendages,  and  enclosing  the  anus  without  very 
well-marked  sutures  between  the  tergum  and  sternum.  Such  a 
description  as  this  would  answer  for  the  tenth  somite  of  almost 
any  form  taken  through  the  remaining  insect  orders  considered. 
Exceptions  may  be  made  in  the  case  of  Panorpa  where  the  whole 
somite  is  long  in  proportion  to  its  width,  and  firmly  chitinized; 
in  forms  as  reduced  and  retracted  as  Hepialus  and  Tabanus, 
where  the  length  is  very  short  in  proportion  to  the  width;  in 
the  female  Pryonoxystus,  where  it  is  retracted  and  membranous, 
yet  long  and  cylindrical. 


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4.  Somite  Eleven. — Somite  eleven,  as  has  been  shown  in 
the  tables,  occurs  the  most  infrequently  of  any  of  the  four 
caudal  somites  studied.  It  is  the  most  characteristic  of  the 
Orthoptera  of  any  order,  although  it  also  occurs  in  certain  gen- 
eralized families.  When  present  it  is  posterior  to  the  tenth, 
surrounds  the  anus,  and  is  niembranous  except  in  such  forms 
as  the  female  grasshopper,  where  its  tergum  is  highly  chitinized, 
and  clearly  separated  from  the  tenth  tergum  by  a well-marked 
suture.  Posterior  to  it  in  those  cases,  in  the  adult,  lies  the 
so-called  twelfth  somite  of  Heymons  showing  in  both  Dissosteira 
and  Melanoplus  (Plate  VI,  Figs.  9 and  10;  1,  10,  13,  and  17,  tl2) 
very  distinct  in  the  female.  This  suture  is  not,  however,  present 
in  certain  nymphal  stages,  according  to  many  investigators, 
even  when  it  appears  in  the  adult,  and  it  would  seem,  therefore, 
to  be  a secondary  modification.  In  other  orders  than  the 
Orthoptera  the  eleventh  somite  is  a short,  homogeneous,  mem- 
branous ring  surrounding  the  anus,  often  distinguishable  with 
difficulty  from  the  anal  lobes. 

5.  General  Statement. — Of  the  four  somites  considered 
above,  it  is  evident  that  the  ninth  is  the  most  specialized  of  all, 
both  by  reduction  of  parts,  by  modification  of  form,  and  by 
lack  of  chitinization — all  three  characteristics  following  upon 
retraction  of  the  caudal  end  of  the  abdomen.  Somite  eight 
changes  least  from  its  form  in  the  primitive  type,  and  in  the 
generalized  Orthoptera,  somites  ten  and  eleven  become  the 
simplest  in  form,  structure  and  substance,  by  specialization  and 
reduction  of  parts. 

6.  Appendage  I.- — This  appendage  occupies  the  most 
extreme  ventro-caudal  position,  and  shows  its  real  connection 
with  somite  eight  only  in  the  saw-flies  and  wasps.  This  pair  of 
appendages  usually  seems  to  be  placed  closely  adjoining  the 
ninth  sternum,  and  is  often  referred  to  as  the  ventral  pair  of 
appendages.  The  ventral  pair  of  ovipositors  of  the  grasshopper 
(Plates  V and  VI)  show  this  relative  position,  although  the 
connection  would  appear  at  first  glance  to  be  with  the  eighth. 
This  is  also  true  in  Appendage  I in  the  female  Lepisma.  This 
appendage  belongs  to  the  eighth  somite,  but  is  often  crowded 
out  of  its  typical  position  by  the  shape,  retraction,  and  function 
of  the  caudal  somites.  The  Hymenoptera  present  another  and 
one  of  the  clearest  cases  of  the  relation  between  Appendage  I 


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135 


and  somite  eight,  as  has  already  been  mentioned  in  another 
conneetion.  This  is  well  illustrated  by  the  female  saw-flies  and 
Vespa  (Plate  XVII,  Figs.  10  and  14)  as  well  as  by  the  generalized 
genus  Lepisma  in  the  male.  The  size  of  these  appendages  varies 
with  their  funetion.  In  the  Orthoptera  they  attain  a good  size 
in  all  the  forms  studied,  in  both  the  male  and  the  female,  being 
more  prominent  in  the  latter.  They  are  often  apparently  small 
tactile  organs  in  the  male  when  Appendages  II  and  III  are 
highly  specialized,  as  in  the  case  of  Benacus,  Euschistus  and 
Anasa,  Appendage  I being  even  less  conspicuous  in  the  females 
of  the  two  last  mentioned  genera,  and  somewhat  smaller  than 
in  the  male.  In  those  groups  having  a complete  metamorphosis 
it  is  either  rudimentary,  as  in  the  female  Hepialus ; absent  alto- 
gether as  is  most*  often  the  case  in  both  the  male  and  female  of 
the  Coleoptera  and  in  female  Lepidoptera  other  than  Hepialus; 
or  specialized  as  so-called  claspers  in  most  male  Neuroptera, 
Mecoptera,  Trichoptera,  and  Lepidoptera  other  than  Hepialus. 
In  the  Diptera,  it  is  rudimentary  in  the  female  Tabanus;  of 
good  size  in  both  the  male  and  female  Tipula,  and  in  the  male 
Tabanus;  and  small  in  both  sexes  in  Calliphora. 

7.  Appendages  II  and  III. — These  appendages  are  prom- 
inent in  those  females  which  have  their  genitalia  specialized  to 
dig  holes  in  which  to  lay  their  eggs,  to  sting,  or  to  perform  some 
other  accessory  function.  Examples  of  these  are  common 
among  the  Orthoptera  and  Hymenoptera  (Plates  V,  VI,  VII 
and  XVII).  Even  here  Appendage  II,  referred  to  above  as  the 
‘‘mesal”  appendage  of  certain  authors,  is  small  or  rudimentary, 
and  it  is  found  to  be  more  often  absent  altogether  in  the  female 
than  in  the  male.  In  the  male  these  appendages  are  most 
specialized  in  connection  with  the  intromittent  organ,  and 
Appendage  II  is  more  often  present  in  the  male  than  in  the 
female.  The  best  examples  of  this  modification  are  seen  in  the 
Hemiptera  and  Coleoptera  (Plates  VIII,  IX,  X,  XI  and  XII). 
Similar  organs,  much  smaller  in  size,  are  also  found  in  Corixa, 
Notonecta,  Corydalis,  Dolerus,  and  Vespa,  made  up,  in  all  these 
cases  of  Appendage  II,  as  well  as  III. 

8.  Appendage  IV. — Appendages  included  under  this  head 
are  most  often  called  the  cerci.  These  are  more  dorsal  in  posi- 
tion than  the  others,  and  seem  in  many  cases  in  adults,  espe- 
cially in  the  Orthoptera,  to  be  as  well  attached  to  somite  ten  as 


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to  eleven.  (Plates  V,  VI  and  VII).  Here  we  have  the  only 
instance  of  the  association  of  one  of  the  genitalia  with  terga 
rather  than  with  sterna,  so  far  as  the  sclerites  are  concerned, 
but  the  membrane  forming  the  tenth  and  eleventh  sterna  is 
also  in  close  contact  with  the  base  of  this  appendage.  Wheeler, 
in  his  work  on  the  embryo  of  Xiphidium,  shows  this  appendage 
attached  .to  the  eleventh  somite.  It  seems  likely  that  variation 
in  the  form  of  these  appendages  accompanies  a change  in 
function.  Evidence  of  this  may  be  noted  in  the  varied  cerci  of 
the  Orthoptera,  Neuroptera,  Mecoptera,  Trichoptera,  and 
Diptera. 

The  main  conclusion  emphasized  is  the  descent  of  the  male 
and  female  genitalia  from  the  anlages  of  abdominal,  pedal 
extremities  of  a myriapod-like  ancestor,  as  seen  in  the  embryos 
of  insects.  The  stylets  upon  which  so  much  emphasis  has  been 
laid  by  investigators,  mainly  represented  by  Heymons,  cer- 
tainly have  little  place  in  the  adult  insect.  That  they  are 
present  in  the  Thysanura  seems  to  have  little  weight  after  one 
has  worked  upon  representatives  not  only  of  that  order  but  of 
many  other  groups,  because  even  where  such  stylets  are  present 
there  are  also  present  far  more  important  structures,  the  above 
mentioned  genitalia.  Even  in  Heymons’s  figures  it  is  clear  that 
the  two  descended  from  entirely  separate  anlages,  and  the 
interpretation  that  the  genitalia  descended  from  the  anlages  of 
stylets  seems  entirely  unnecessary,  and  in  fact,  in  one  case  at 
least,  entirely  wrong. 

That  there  are  traces  in  the  adult  insect  of  ten,  eleven,  or 
possibly  twelve  somites,  would  seem  but  natural  considering  the 
probability  of  a far  greater  ancestral  number,  but  only  somites 
eight,  nine,  ten,  and  eleven  bear  a direct  relation  to  the  genitalia. 


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V.  EXPLANATION  OF  PLATES. 

Abbreviations. 

The  following  plates  include  figures  of  the  posterior  somites  and  appendages 
of  the  male  and  female  forms  of  the  insects  studied.  Other  accessory  points,  such 
as  external  openings  and  their  connections  with  their  ducts,  are  shown  wherever 
possible.  Everything  has  been  carefully  and  clearly  labeled  according  to  the 


following: 

I 

. . .Appendage  of  Somite  Eight. 

Cop.... 

. . . Bursa  Copulatrix. 

II.. 

. . .Appendage  of  Somite  Nine. 

Cp 

. . . “Copulatory  sacs. 

Ill 

. . . Appendage  of  Somite  Ten. 

D 

. . .Ejaculatory  Duct. 

IV 

, . .Appendage  of  Somite  Eleven. 

G 

tl-tll.. . 

, . .Terga  One  to  Eleven. 

Ov 

tI2 

, . .Terga  Twelve  of  Heymons, 

R 

sl-sll... 

, . . Sterna  One  to  Eleven. 

Rp 

A 

. .Anus. 

S 

. . . Spermatheca. 

Ab 

. .Anal  Brush. 

Sp 

Ap 

. . Apodeme. 

St 

. . . Stylet. 

As 

. .Appendages. 

Tr 

. . .Tracheae. 

C 

. .Cerci. 

V 

. . .Vagina. 

Con 

. .Conjunctiva. 

Vd 

. . . Vas  deferens. 

Pl.\te  IV — Primitive  Type  and  Thysanura. 

Primitive  type.  Fig.  1,  ventral  view. 

Machilis  sp.,  2,  9,  mesal  view;  3,  9,  ventral  view;  4,  d^,  ventral  view. 

Lepisma  saccharina,  5,  9,  dorsal  view;  6,  9,  ventral  view;  7,  9,  mesal  view;  8, 
9,  ventral  view;  9,  cf,  dorsal  view;  10,  cf',  ventral  view;  11,  d',  mesal  view; 
12,  13,  d,  ventral  views. 


Plate  V — Orthoptera. 

Periplantea  orientalis,  1,  9 , lateral  view;  2,  9 , dorsal  view;  3,  4,  5,  6,  11,  9 , caudal 
views;  8,d^,  ental  and  mesal  view;  9,  9,  ental  view;  10,  d,  ventral  view;  13, 
d,  mesal  view;  16,  d,  dorsal  view. 

Dissosteira  Carolina,  7,  9 , dorso-caudal  view. 

Mantis  sp.,  12,  9 , lateral  view;  14,  9 , ventral  view;  15,  9 , ental  view. 

Melanoplus  differentialis,  17,  d,  dorso-caudal  view. 

Plate  VI — Orthoptera. 

Melanoplus  differentialis,  1,  9,  lateral  view;  2,  9,  mesal  view;  4,  9,  mesal  view; 
5,  9,  lateral  view;  6,  d,  lateral  view;  7,  9,  ental  view;  9,  d,  ventral  view; 
11,  12.  d,  mesal  views;  13,  d,  dorsal  view;  16,  d,  dorsal  view;  17,  9,  dorsal 
view;  18,  d,  lateral  view;  19,  9,  ventral  view. 

Dissosteira  Carolina,  3,  d,  ental  view;  8,  d,  caudal  view;  10,  9,  lateral  view;  14, 
9 , ental  view;  15,  9 lateral  view;  20,  9 , mesal  view. 

Plate  VII — Orthoptera. 

Gryllus  pennsylvanicus,  1,  5,  10,  caudal- views;  2,  lateral  view;  3,  6,  ventral  views; 
7,  9,  dorsal  view;  8,  d,  lateral  and  ental  views;  9,  d,  ventro-caudal  view; 
10,  d,  caudal  view;  11,  d,  ventral  view;  12,  d , dorsal  view;  15,  9 , mesal  view. 
Dissosteira  Carolina,  4,  d,  caudal  view. 

Xiphidium  ensiferum,  13,  d,  dorsal  view;  14,  17,  d,  caudal  view;  16,  d,  ventral 
view;  18,  9 , dorso-lateral  view;  19,  9 , dorsal  view. 


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141 


Plate  VIII — Hemiptera. 

Tihicen  septemdecim,  1,  8,  cf,  ventral  views;  3,  12,  9,  lateral  views;  9,  cf,  dorsal 
view;  15,  cT,  lateral  view;  18,  9,  dorsal  view. 

Corixa  sp.,  2,  9,  ventral  view;  19,  9,  dorsal  view. 

Benacus  griseus,  4,  13,  14,  9,  lateral  views;  7,  9,  ventral  view;  6,  9,  dorsal  view. 

Notonecta  undulata,  5,  22,  cT,  lateral  views;  10,  11,  dorsal  views;  16,  17,  21,  cf , ven- 
tral views;  20,  9 , ventral  view. 

Plate  IX — Hemiptera. 

Anasa  tristis,  1,3,  9 , dorsal  views;  2,  7,  8,  9 ventral  views;  5,  9 , dorsal  and  mesal 
views. 

Corixa  sp.,  4,  6,  10,  9 , ventral  views;  11,  14,  9 , dorsal  views. 

Notonecta  undulata,  9,  9 , ventral  view. 

Benacus  griseus,  12,  18,  cT,  ventral  views;  13,  cT,  lateral  view;  15,  cf , dorsal  view; 
16,  d',  mesal  view;  17,  ci’,  lateral  and  ental  view. 

Notonecta,  19,  9 , ventral  view. 


Plate  X — Hemiptera. 

Euschistus  variolarius , 1,  9 , dorsal  view;  2,  6,  9 , ventral  view;  3,  8,  cf,  dorsal  views; 
9,  d,  ventral  view;  10,  d,  mesal  view. 

Anasatristis,  4, 17, d^, ventral  views;7.cf, ental  view;  14,6^,  caudal  view;  15,6^,  lateral 
view;  18,  d,  dorsal  view;  20,  d,  mesal  view. 

Notonecta  undulata,  5,  9 , dorsal  view. 

Benacus  griseus.  11,  9 , caudal  view;  12,  9 , mesal  view;  13,  16,  ventral  views;  19,  d, 
ventral  and  ental  view. 


Plate  XI — Neuroptera,  Mecoptera,  Trichoptera. 

Corydalis  cornuta,  1,  d,  ventral  view;  2,  cf,  dorsal  view;  4,  d,  ventral-caudal  view; 

5,  9 , dorsal  view;  6,  9 , ventral  view;  15,  9 , lateral  view;  19,  9 , caudal  view. 
Panorpa  luguhris,  3,  8,  21,  cf,  lateral  views;  9,  cf,  mesal  view;  11,  9 , ventral  view; 
12,  18,  dorsal  views;  14,  9,  ental  and  ventral  views;  16,  cf,  ventral  view;  17, 
cf,  mesal  and  ventral  views;. 

Nerophilus  californicus,  7,  d,  ventral  view;  10,  cf , dorsal  view;  13,  cf , caudal  view. 


Plate  XII — Coleoptera. 

Harpalus  caliginosus,  1 2,  7,  9 , dorsal  views;  4,  5,  8,  9 , ventral  views;  9,  9 , mesal 
view;  10,  cf,  lateral  view;  11,  13,  cf,  dorsal  views;  17,  23.  cf,  ventral  views. 

Cyhister fimbriolatus.  3,  18,  cf,  ventral  views;  12,  cf,  mesal  view;  14,  21,  9,  dorsal 
views;  15,  9 , lateral  view;  19,  cf , dorsal  view;  20,  9 , ventral  view. 

Doryphora  decemlineata,  6,  cf,  ventral  view;  16,  9,  ventral  view. 

Plate  XIII— Coleoptera. 

Hydrophilus  triangularis,  1,  14,  cf , dorsal  views;  6, 15, 16,  cf,  ventral  views;  7,  9 , ental 
view;  11,  9 , ventral  view;  20,  9 , dorsal  view. 

Doryphora  decemlineata,  2,  13,  18,  cf,  ventral  views;  4,  5,  dorsal  views;  10,  22,  9, 
dorsal  views;  17,  9 , ventral  view;  24,  9 , ventral  and  ental  views. 

Cyhister  fimbriolatus,  3,  9 , ental  view;  8,  cf , dorsal  view;  :,  9 dorsal  view;  12,  21, 
cf , lateral  views;  19,  9 , ventral  view. 

Harpalus  caliginosus , 23,  9 , ental  view;  25,  9 , lateral  and  ental  view. 


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Plate  XIV — Lepidoptera. 

Prionoxystus  rohinice,  1,  cf,  dorsal  view;  2,  11,  cT,  ventral  views;  3,  9,  cT,  lateral 
views;  4,  cf , mesal  view;  of  genitalia;  5,  9 , dorsal  view;  6,  9 , entalviewof  S.  8; 
8,  15,  9,  ventral  view;  12,  9,  ventral  view  of  8th  segment;  14,  9,  ental  and 
lateral  view;  17,  9 , lateral-ental  view. 

Hepialus  humuli,  7,  9 , caudal  view;  10,  cf,  caudal  view;  13,  9 , .dorsal  view;  16,  9 , 
ventral  view;  19,  ci’,  lateral  view;  22,  9 , lateral  view. 

Anosia  plexippus,  18,  9 , lateral  view. 

Protoparce  Carolina,  20,  cf,  lateral  view. 

Agrotis  ypsilon,  21,  9 , lateral  view. 


Plate  XV — Lepidoptera. 

Agrotis  ypsilon,  1,  cT,  dorsal  view;  6,  9 , dorsal  view;  8,  d^,  lateral  view  of  genitalia; 
11,  cf , ventral  view. 

Protoparce  Carolina,  2,  9,  dorsal  view;  9,  cf,  dorsal  view;  12,  cT,  ventral  view; 

14,  cf,  lateral  view;  15,  9 , ventral  view;  16,  9 , lateral  view. 

Anosia  plexippus,  3,  9,  dorsal  view;  4,  9,  ventral  view;  5,  10,  cf,  ventral  views; 
7,  d^,  dorsal  view;  13,  cf,  lateral  view. 


Plate  XVI — Diptera. 

Calliphora  viridescens,  1,  cT,  dorsal  view;  2,  cT,  ventral  view;  3,  7,  cf , lateral  views; 
4,  9 , dorsal  view;  6,  9 , ventral  view. 

Tabanus  sulcifrons,  5,  13,  cf,  ventral  views;  8,  cf,  detail;  9,  cf,  dorsal  view;  10,  9, 
caudal  view;  11,  15,  9 , dorsal  views;  12,  14,  9 , ventral  views. 

Tipula  ahdominalis , 16,  9,  ventral  view;  17,  9,  dorsal  view;  18,  22,  cf,  ventral 
view;  19,  9 , caudal  view;  20,  21,  cf , dorsal  views. 

Plate  XVII — Hymenoptera, 

Dolerus  unicolor,  1,  9 , dorsal  view;  5,  cf , mesal  view;  9,  19,  cf , dorsal  views;  13,  15, 
cf,  ventral  views;  14,  16,  20,  9,  ventral  views. 

Vespa  maculata,  2,  11,  9 , lateral  views;  3,  4,  8,  18,  cf,  ventral  views;  6,  17,  9 , dorsal 
views;  7,  cf,  mesal  view;  10,  21,  9,  ventral  views;  12,  22,  cf,  dorsal  views. 


Annals  E.  S.  A. 


VoL.  XI,  Plate  IV. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VOL.  XI.  Plate  V. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI,  Plate  VI. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI.  Plate  VII. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI.  Plate  VIII. 


Anna  Grace  Newell 


Annates  K.  S.  A. 


VoL.  XI,  Plate  IX. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VOL.  XI,  Plate  X. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI.  Plate  XI. 


Anna  Grace  Newell 


Annals  E-  S.  A. 


VoL.  XI,  Plate  XII. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI,  Plate  XIII. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI,  Plate  XIV. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI,  Plate  XV. 


Anna  Grace  Newell 


Annals  H-  S.  A. 


VOL.  XI,  Plate  XVI. 


Anna  Grace  Newell 


Annals  E.  S.  A. 


VoL.  XI,  Plate  XVII. 


Anna  Grace  Newell 


